Not posting this as a promotion — I’m more interested in sharing the architecture and getting feedback on whether the approach makes sense.
Design overview
All encryption happens on-device (server never sees plaintext)
Master key derived using Argon2id (memory-hard, device-tuned)
Per-item keys derived via HKDF (key separation per item)
Data encrypted using AES-256-GCM with associated data binding (userId, itemId, type)
Sharing model
This was the most challenging part. Instead of server-side re-encryption:
Each user has an X25519 keypair
Each share generates a fresh symmetric key (DEK)
DEK is encrypted using recipient’s public key (ECDH + HKDF)
Server stores only ciphertext + wrapped key
Implementation challenges
Handling crypto without blocking UI (isolates / background work)
Managing key lifecycle in memory (auto-lock, clearing sensitive data)
Designing UX that stays simple while enforcing strict security rules
Keeping state consistent across sessions without leaking secrets
Open questions / things I’m evaluating
Public key distribution trust (currently email-based lookup → considering pinning/fingerprints)
Key rotation strategy for users
Whether to move authentication toward a PAKE (SRP / OPAQUE)
Tradeoffs around metadata leakage
I’ve made the project open-source here: https://github.com/TrendySloth1001/keepit/releases
If anyone has experience with E2E systems, secure storage, or crypto-heavy apps, I’d really appreciate any feedback or criticism — especially on the sharing flow and key management.
